1. Field of the Invention
This invention relates to quantitative measurement of blood flow, and more specifically, quantitative measurement of blood flow using Magnetic Resonance Imaging
2. Description of Related Art
Angiography, or the imaging of vascular systems by Magnetic Resonance (MR) has been demonstrated using a variety of techniques based on time-of-flight phenomena and the phenomena of velocity-induced phase shifts. See Dixon WT, Du L. N., Faul D. D., et al. "Projection Angiograms of Blood Labelled by Adiabatic Fast Passage" in Magn. Reson. Med, 3:454, 1986; Nishimura D. G., Macovski A., Pauly J. M., et al. "MR Angiography by Selective Inversion Recovery" in Magn. Reson. Med, 4:193, 1987; Laub G. A., Kaiser W. A. "MR Angiography with Gradient Motion Refocusing" in J. Comp. Asst. Tomogr., 12:377, 1988; Dumoulin C. L ., Cline H. E., Souza S. P., et al. "Three Dimensional Time-of-Flight Magnetic Resonance Angiography Using Spin Saturation" in Magn. Reson. Med., 11:35, 1989; Keller P. J., Drayer B. P., Fram E. K., et al. "MR Angiography Via 2D-Acquisition, but Yielding a 3D-Display: A Work in Progress" in Radiology, 173:527 (1989); Wedeen V. J., Meuli R. A., Edelman R. R., et al. "Projective Imaging of Pulsatile Flow with Magnetic Resonance" in Science, 230:946, 1985; Dumoulin C. L., Hart H. R. "Magnetic Resonance Angiography" in Radiology, 161:717, 1986; Dumoulin CL, Souza S. P., Hart H. R. "Rapid Scan Magnetic Resonance Angiography" in Magn. Reson. Med., 5:238, 1987; Dumoulin CL, Souza SP, Walker MF, et al. "Three Dimensional Phase Contrast Angiography" in Magn. Reson. Med., 9:139, 1989.
Clinical use of several MR angiographic techniques in the head and neck have been recently reported See Masaryk T. J., Modic M. T., Ross J. S., et al. "Intracranial Circulation: Preliminary Clinical Results with Three-Dimensional (Volume) MR Angiography" in Radiology, 171:793, (1989); Masaryk T. J., Modic M. T., Ruggieri P. M., et al. "Three-Dimensional (Volume) Gradient-Echo Imaging of the Carotid Bifurcation: Preliminary Clinical Experience" in Radiology, 171:801,(1989); Wagle W. A., Dumoulin C. L., Souza S. P., et al. "3DFT Magnetic Resonance Angiography of Carotid artery and Basilar Artery Disease" in Am. J. Neuroradiology, 10:911 (1989).
Some degree of quantification has proven possible with some phase sensitive methods. See Walker M. F., Souza S. P. and Dumoulin C. L. "Quantitative Flow Measurements by Phase Contrast Magnetic Resonance Angiography" in J. Comp. Asst. Tomogr. 12:304 (1988); Nayler G. L., Firmin D. N. and Longmore D. B. "Blood Flow Imaging by Cine Magnetic Resonance" in J. Comp. Asst. Tomogr. 10:715 (1986).
While the above methods of MR angiography can provide excellent morphological detail, it is frequently difficult to obtain quantitative flow information. This is because a given volume element, called a volume pixel ("voxel") may contain a distribution of velocities which interfere with one another in the detection or data collection process.
Several non-angiographic techniques have been proposed though they are not common. For example, bolus tracking in which the bulk movement of excited spin magnetization is monitored, has been reported. This has been done with boluses of inverted spin magnetization. See Morse O. and Singer J. R. "Blood Velocity Measurements in Intact Subjects", Science 170:440 (1970). Boluses of saturated spin magnetization were described by Wehrli F. W., Shimakawa A., MacFall J. R., et al. "MR Imaging of Venous and Arterial Flow by a Selective Saturation-Recovery Spin Echo (SSRSE Method" in J. Comp. Asst. Tomogr. 9:537 (1985), Edelman RR, Finn J. P., Wentz K., et al. "Magnetic Resonance Angiography and Flow Quantitation in the Portal Venous System" in Proceedings of the 8th Annual meeting of the Society of Magnetic Resonance in Medicine, Amsterdam, 1899, 208. Boluses of transverse spin magnetization were also monitored by Shimizu K., Matsuda T., Sakurai T., et al. "Visualization of Moving Fluid: Quantitative Analysis of Blood Flow Velocity Using MR Imaging" in Radiology, 159:195 (1986). An alternative approach is the use of flow-encoding gradients which provide a motion-dependent phase shift as disclosed in Feinberg D. A., Crooks L. E., Sheldon P., et al. "Magnetic Resonance Imaging the Velocity Vector Components of Fluid Flow" in Mag. Reson. Med. 2:555 (1985); Hennig J., Muri M., Brunner P., et al. "Quantitative Flow Measurement with the Fast Fourier Flow Technique" in Radiology, 166:237 (1988); Souza S. P., Steinberg F. L., Caro C., et al. Proceedings of the 8th Annual Meeting of the Society of Magnetic Resonance in Medicine, in Amsterdam, 1989, pg. 102; Moran P. R. "A Flow Velocity Zeugmatographic Interlace for NMR Imaging in Humans" in Mag. Reson. Imag. 1:197, (1982).
Fourier-encoded velocity measurements proposed by Feinberg et al. and Hennig et al. employ a spin-warp imaging pulse sequence which uses flow sensitive phase-encoding gradient pulses to quantify velocity.
Feinberg et al. and Hennig et al. provide a spatial representation of the velocity of flowing blood, but in only a single dimension. There is a need to provide a noninvasive method of determining the flow of fluids in selected vessels which is accurate and reliable.
In addition, fluid flow measurements are a good indication of hemodynamic properties of a given vessel. These hemodynamic properties are important in Medical Applications such as in diagnosing a variety of abnormalities and diseases. It would be useful to be able to acquire the hemodynamic properties without the use of invasive techniques.